Method and machine for testing thin strips



Oct. 18, 1932. J v s E 1,882,802

METHOD AND MACHINE FOR'TESTING THIN.STRIPS Filed Dec. 27, 1926 5 Sheets-Sheet 2 author amp Oct. 18, 1932. J v s R 1,882, 802

METHOD AND MACHINE FOR TESTING THIN STRIPS Filed Dec. 27, 1926 Sheets-Sheet 3 Patented Oct. 18, 1932 VP'A'TLENT o F IcE JEAN v. GIESLER, OEKNXVILLE, r'nvvnssma ASSIGNOR, BY minstri: ASSIGNMENT& TO THEFULTON sYLPHo comPANY, OF KNOXVILLE, TENNESSEE,'A ooarom ron or DELAWARE i g METHOD AND MACHINE FOR TESTING THIN' STRIPS Application ni a December 27, 1926. Serial No. 157350.

This invention relates to a method and machine for testing pieces `under' repeated, reversed bending stresses.

It has heretofore been customary in studying the endurance limit of m'etals to, subject the test pieces to repeated and completely reversed bending stresses in a machine where*- in the test piece constitutes a'loaded rotat- 'able beam, the fibers of the test piece being thereby alter'nately subjectedto stresses of tension and compression.

It is an object of this invention to provide a method" and machine for studying endurance limit, by subjecting testpieces -to rey peated V and completely` revejrsed i bendng stresses, whereinthe test pieces are nottreated as loaded rotatable beams and yet where'- in the fibers of the test pieces are alternately subjected to stresses of tension and compression in a simple, accurate and eflicient manner. i a V Anotherobject of this 'invention is to provide a method and machine of the character described which %provides for readyadjustment so that test 'pieces may be subjected to 'difierentmagnitudesof stresses, or to a uniform ora variable' tensilgstress in conjunction with the bending istresses Other objects of theinventionrelate toa method and machine of the character described which avoid complex stresses sothat the total Stress to whichthestest piece -is subjected'may be readily calculated by known formula; and in which the variables of the formulae may be accurately measured; which avoid localized stresses or' unintended or' in- (leterminate stresses which may upset'the 'accurate measurement of the 'variables or` the accurate deternination of the stress-which the character described which enablesthe test i pieceto be subjected to simple bending stresses,` or to bending stresses in (cojn- Juncton wth a *constant i tensle Stress,

`treatments of 'studied i v or to bending stresses in conjunction with a variable tensile stress`,. which may vary from 'zero to a maximum or between predetermined ,minimum and'maximum values, whichstre'sses may' bevaried in magni- 1 tude' through a wide range so that the relation of the number of complete reversals of bending Stress to-the magnitude of the stresses may be readily ascertained for-the' plotting'of an S-N diagram 'and a study of 1 endurance limits under a wide variety of condit'onsin orderthahthe relative capacity'of different metals and the eflect of various the same may be readily Other objects will appear as'the description of the invention proceeds;

The invention is' capable of being carried out in a variety of ways and of being embod- *ied in a variety ofmechanical constructions one of which constructons has been shown on the accompanying drawings, but it is to be expressly understood that the drawings i are for purposes of illustrationonly and are not to be construed as a definition 'of the limi its of the invention, reference being had to the appended claims for that purpose.

Referring in detail to the drawings, wherein the same reference characters are employed to designate corresponding. parts in the several figures:

Fig. 1 is a more or tion 'of a machine embodying the present invention and adapted to carry out the method of the present invention; a

Fig. 2 is a side elevation of the machine ot-Fignl; g y i a Fig.` 3 is a rear elevation of the machine of Fig. 1; i

Fig. 4 is an enlarged front elevation of the sectors'by whichthe 'test piece is subjectcd to repeatedand completely reversed bending stresses; and

Fig. 5 is a further enlarged, partly sectional View of means for imposing and adjusting the magnitude of the tensilestresses.

In studying the i relative worth of different materials and the effects thereon' ofvarious characters of treatments in the Capacity k of such materials towithstand repeated flexless schematic elevai ure without rupture. it is desirable to sub ject test pieces of the materials under consideration or subjected to the treatments under consideration to repeated, completely re- I versed bending stresses. It is also desirable to be able to vary the magnitude `of the stresses within considerable limits and to consder the effect of constant or varable tensile stresses in conjunction with'the reversed bending sti-esse& In accordance with the present invention a method and machine have been provided which are simple and easy of operation and adjustnient so that different' test pieces may be readily tested under a wide variety of conditions and the magnitude of the st'resses accurately and simply 'determined. As the method of this invention will be 'more readily understood after the eX- planation of the Construction and operation 'of a suitable means for applying the bending 'stresses, reference will first be had to the machine illustrated on the drawings;

In the form shown, the test piece 10 in'the form of a strip of any suitable width and length *is suitably clamped adj acent its opposite ends'to a 'pair of opposed sectors 11 and -12,of equal radius of curvature, and mountthe test piece 10 'first around 'one sector and then around the other sector in 'alternation as long as the machine s in operation. If

- the 'connectingrods 1-9- and make equal angles with the center line of reciprocation 'of the crosshead 23 the movements of the sectors are exactly equal andthe test piece is subjected -only 'to a simple 'bending Stress, and if the sectors -are of exactly equal radius the stresses are .equally reversed' because, as thepiece is alternately bent around the respective sectors, all portions of the test piece which are subjected to the reverse bending` are bent equal amounts in opposite directions. As the magnitude of the bending Stress 'is determined by the radius of curvature of the sectors, the .Stress 'to which the test piece is sub ected may then be readily calculated by the formula, S where T :equals the thio'kness of the piece, B equals the radius of the arc into which the test piece is bent taken from the neutral aXis of the piece, and E equals Young 's modulus of themetal under test'. WVhere the thiclzness of th'epiece'is very small in "comparison with the raciius of curvature into which it is bent, it is permissible to take the radius of the sector around which the piece is bent as the R of the formula. i

By varying the sizes of the sectors, varying magnitudes of stresses may be obtained.

By imposing a constant stress on the test' piece in the direction of its length during the test, the'eiiect of a constant tensilestress in conjunction with the repeated and completely reversed bendingstresses may be ascer- .tained. The efiect of a varying tensile stres:: in con uncton' with the repeated and comp pletely reversed bending stresses can be studed by varying the amount of the Stress in the 2 direction of the length of the test piece in any suitable way. Thus "the relative movements of the sectors canbe varied by varying the relative angularity of the connecting rods 19 and 20 to the center line of reciprocation of n the crosshead 23. Therefore, with a knowledge of' the number' of reciprocations of the crosshead 23 which 'produce rupture of the test pieces under given magnitudes and conditions of Stress the endurance limit or the S-N dia-gram of test pieces of differentmaterials or previously subjected to different treatments can be readily and accurately determined. r y

The machine for carrying out the above method and for embodying the above prin- -ciples may be of any suitable Construction. In 'the form shown, a base 25 of any suitable size, Construction and material is provided with a pair of upstanding brackets 26 and 27 which at their upper extremities carry the pivots or stub shafts 13 and14 upon' which the sectors 11 and 12 are mounted. v Brackets 26 and 27 are mounted for guided 'linear movement toward: and from eachother, at i right angles to the axes 13 and 14, in any suitable way, being shown .as provided with an eXtended hearing on the upper surface of the base 25 and having depending ri'bs 28 which make 'a sliding *fit in suitable slots in the top of said base. Means are provided formoving said brackets 26 and 27 toward and from each other, said means being pref erably so; constructedas to enforce equal and opposite movements of said brackets so that e said brackets will always be in proper posi- ,tionfor the `coaction of a pair of sectors of equal radius of curvature, to whatever position theymay be adjusted. In the form shown, each of said'brackets carries a depending lug 29 havingan interiorly thread- .ed' aperture, and mounted in 'the base 25 is a long threadedrod 30 having right 'and left hand threads of equal pitch 'at its opposite ends, the lugs 29 having corresponding right ,and left hand threads for coaction with the threads on said rod 30. Hence when the rod 30 is rotated the brackets 26 'and 27 will be made to approach or recede from each other by equal increments, depending'upon. the dirrod 30. a

rection of 'rotation of the unitary threaded In .orderthat the brackets 26 'and 27 may bothbe moved together 'in either direction in order to dispose the oonnecting rods 19 and 20 at different relative angles to the cen- -ter line of reciprocation of thecrosshead 23,

means are also provided for shifting the threaded rod 30 bodily n the drection of its length. In the form shown, oneend of said rod is reduced in diameter as shown at 31 ,and has a hearing in an extcriorly threaded block 32 which engages in, an interiorly threaded aperture 33 in the end wall of the bas`e30. Theoppositeend of the rod 30 has a portion 34 of reduced cross ,section which has hearing in an exterorly threadedblock 35 which engages in an interiorly threaded aperture 36 in the end wall of the base 25. Reduced portion 34 extends to the enterior of the block 35 where it may be squared as shownat 37 'to receive a crank or other suit able means for rotating said red 30. The

threaded rod30 is normally prevented from endwise movement by the engagement of 'its shoulders38gand 39 with the ends of the bearingblocks 32 and '35 respectively, but

may be moved endwise by adjustment of said bearing blochs in thethreaded apertures 33 anc-`36 respectively.` Said hearing blocks may be retained in their adjusted position by lock nnts 40.

- Bracket 42 also carries a` rearwardly extending-bracket43 which provides bearings 44 'for agshaft 45 on which isimounted a pulley 46 or any other suitable means forrotating said shaiit. Shaft`45 at its nner end-carres a crank disk or block 47 whchis preferably so construc'ted as to provide adJuStment for +1 n J' Ag the radus OI rotaton or the CI ank pin i being shown as provided with a dovetail way 49 and a plurality of clamping` screws 50 to 'the end thatthe crank pin may be variously positioned in s'aid way clamped in adjusted position. Extendng from the crank pin 48his a connecting rod 51 pivotedto the erosshead 23 at 52.

Means are preferably `'provided tor count ing the number of rotations of the shaft 45, and therefore the number of reciprocations of the crosshead 23. Any suitable meansm'ay be provided for this purpose, the shaft 45 being' shown as provided with' a worm 53 which meshes with' a worth-'wheel 54 carred' by the shaft 55 of a counting mechanism 56, of any suitable Construction, supported `on a lateral extension 57 of the bracket 43.

s Bracket 43 is preferably mountedfor"` versaid sectors.

tical adjustment on the bracket 42 so that as sectors of different radii'of curvature are .mounted on the pivots or stub shafts 13 and 14, the crosshead 23 and its driving mech'anism 'may be adjusted to the end that the medial points of said sectors may be in opposition when the crosshead is at the middle of its stroke. In the form shown, the bracket 42 is provided with an elongated vertical slot 58 in which 'a' projection or rib 59 on the bracket 43 may slide, and suitable clamping screws 60 are provided for retaining the bracket 43 in adjusted position. Bracket 42 also has an elongated vertical slot 61 of sufficient eXtent to provide for the reciprocating movements of the pivot pin 52, by which the crank '51 is connected tothe crosshead 23, for all positions ofadjustment of the driving mechanism for the crosshead.

Bracket 42 is 'also fixedly Secured to the base (35 25 in any suitableway as by a plurality of clamping screws 62.

Any suitable means are provided for ati taching the test piece to the sectors 11 and 4 12. In the form shown, each of said sectors ;50

carries an arm 63 which is pivoted to an arm of the sector, as at 64, and each of said arms carries a clamping member 65 and a set screw 66 whereby the test piece may be clamped to the end of the arm 63, which is preferably so shaped as to constitute a continuation of the curvature of the periphery of the sector when the arm is disposed alongside of the .edge of the sector. l Vhen .the test piece breaks under the repeated bending stresses the arm 63 will move away from its sector under the action of inertia as the sector oscillates, and advantage may be taken of this relative movement of the arm to stop the &DO

machine or to give notice of the rupture of thetest piece, as by the closing of an electrical contact when arm 63 moves away from its normal position. If desired, the movement of the arm 63 away from normal position upon the rupture of the test piece may be positively etfected by attachinga light spring thereto so as to insure the desired movement of the arm63 upon rupture of the test piece. i

When it is desired to study the ettect of a constant tensile Stress in conjunction with the 'bending stresses, or a variable tensile Stress in conjunction with the bending -stres ses, one or both of each pair` of sectors are preferably provided with means for imposing a constant or a variable tensile Stress, as the case may be, on the test piece being subjected to the reverse bending action of In the structure shown in Fig. 5 means are provided whereby a constant ten sile stress may be imposcd on the test piece and said means may be operated in conjunction with the disposition of thesectors so that the ,connecting rods 19 and 20 are at different angles to the center line of reciprocation of the crosshead 23 for imposing a variable tensile stress on the test piece. As shown in EFig. 5, the sector is provided with` a cylindrical recess 67 which houses a coil spring' 68, and the pvoted arm`63 carries a *screw E 69 which works in a threaded aperture of said arm 63. The inner endofsaid screw 69 is provided, in any' sutable way, with a collar 7 1 which bears against the col spring 68,' the opposite end of which seats in the bottom of 69 it may be made to project into the recess 67 to a greater or lessextent, and if a test piece is clamped to the arm 63 so as to prevent relative movement of said arm with respect to the sector, the 'spring 68. will be put under various extents of compression whereby it will react to impose a predetermined tension on the test piece subjected to tle reverse bending stresses. It the angularity of the two connecting rods 19 and 20 to the center line of reciprocation of the crosshead 23 is equal, the tensile stress imposed by the spring 68 will be constant. If the brackets 26 and '27 'are adjusted, however, so that said conjusting the spring 68, the variation in the tensile Stress imposed thereby on the test piece may be from Zero to a given maximum or from a given minimum to a given maximum, and bysuitably designing the spring mechanism shown in Fig. 5, the extent of these minimum and maximum values oI" the i 'tensile stress ma be varied within the 'desired limits.

In operation the pulley 46 is driven from any suitable source of power and by its rotation of the shaft 45 the crank 47, 48 drives the connecting rod 51 to reciprocate crosshead 23 in its ways 24. As the crosshead 23 reciprocates, the connecting'rods 19 and 20 rock the sectors 11 and 12 about their pivots or stub shafts 13 and 14, the direction of rotat-ion of the two sectors around their respec 'posite extremities to said sectors, is alternately wrapped around one sector and then Wrapped around. the other sector, moving bodily or reciprocating in opposite directions in a sinuouspath that is' fiXedin space and provides reverseddirections of curvature so that the test piece is movlng n a rogressively changing ogee curvature, the simple'repiece is bent in opposite directions is the same.

The test piece may thus be subjected to re- .peated and completely reversed bending stresses until it ruptures. The number of repetitions of revrsals of bending is known by noting the number of revolutions of the shaft 45 as indicated by the counter 56, while the magnitude of the ben'ding Stress to which the test piece is subjected can be simply calculated from the aforesaid formula by knowing the thickness of the test piece, the radius ot the sectors and Young s modulus of the piece under test. Therefore the endurance limit of the test piece may be readily determined. i v u By using different pairs of sectors having different radii of curvature the endurance limt of test pieces under different stresses can be determned, and from this dat-a the 'S -N' diagram may be plotted. To this end the sectors 11 and 12 are mounted ontheir pivot pins or stub shafts 13 and 14 and their extension arms 15 and 16 are-connectedto the connecting rods 19 and 20 in any suitable way to facilitate ready replacement.

When mounting a different pair of sectors on the pivots 13 and 14 the supports 26 and 27-should be adjusted to separate said pivots for sectors of larger size and to cause said pivots to approach each other for sectors of smaller size, so that said pivots will be spaced apart a distance substantially equal to the sum of the radii of the sectors plus .the thickness of the test piece. Moreover, in so adjusting said pivots, their movements should be equal and opposite so that they shall be equally spaced from the center line of reciprocation of the crosshead 23. This adjustment is effected by rotating the threaded rod j- 30, as by the application of a crank to squared end 37, and the two brackets 26 and 27 will be made to approach or recede from each other by equal increments by reason of the p equally pitched right and left hand threads i with the threaded lugs on thebracketsv Therefore this method and apparatusaf ford a readymeans for studying and com-e 3 paring the endurance limit and characteristics of difierentmaterialsor of any given material under different conditions of heat treatment, cold i working, annealing,. etc. The 'efiect of a constant tensilestrength in conjuncton With the repeated and reversed bending stresses can similarly be determined by imposing an initial stress in the direc- V tion of the length of the test piece by adjusting thespring 68 after the test piece has been clamped .onto the sectors. The efiect of a variabie tensile stress in conjunction with the` repeated and reversed bending` stresses can be ascertained by rotating hearing blocks 32 and 35, after the lock nuts 40 have been loosened, so asto shift the rod 30 and the brackets %and 27 in one direction or the. other so that the connecting'rods 19 and 20 make unequal angles with the center line of reciprocation of crosshead 23. In this posi-` tion of adjustment the movements of the sectors are unequal and, with a suitable tension imposed on the test piece through spring 68, a variable tensile force is exerted on the test piece as the latter is bent back and forth various conditions of constant or variable tensile stress as well as under conditions or simple bendingstress.

Provision is also made whereby the length of stroke of crosshead23 may be varied and therefore the eXtent of the test piece which is wrappedback and forth upon the pairs of ectors may be adjusted. V lt Will therefore be perceived that a method'and machine for subjecting test pieces to repeated and completely 'reversed bending stresses have been provided wherein the 'test piece is not rotated as aloaded beam and yet wherein the fibers of thetest piece are` repeatedly and alternately subjected toequal conditions of compression and tension under bending, these stressesbeing equal in opposite directions and' equally applied throughout so far as the test piece is bent reversely. The method and machine mor'eover readily provide for the use of a' wide variety of magnitudes of bending stress, and the study of the effects of constant and variable tensile stresses in conjunction with the bending stresses of difierent magnitudes., e

It will also be perceived thatthe method and machine are such as to'introduce no com-,

pleX or indeterminate stresses, so that the magnitude ofthe stresses imposedmay be simply and accurately determined by the use of simple formulae the variables of which may be readily and accurately ascertained. The machine is also simple in construction and easy to operate and adjust so that the work of running a large number of tests una der Varying conditions is greatly simplified. Furthermore, the method and machine are particularly suitable for testngrelatively thin strips of metal, of the order of ten -thoustresses which are repeatedly and complete-.

ly reversedthe machine is capable of use in studying morecomplex stresses. Thus more complex bending stresses may be studied by the use of pairs of sectors which are of unequal size, or by the use of sectors whose operative surfaces, are not arcs of circles, etc.

While the preferred method and the illustrated embodiment 'of the machine have been described with considerable particularity, it is to be eXpressly understood that the in-: vention is not restricted'thereto, 'as the invention is capable of being carried out in' other ways and embodied in other machines', as will be readily apparent to those 'skilled in the art, while changes may be madein the details 'of Construction, arrangementand proportion of parts without departing from the spirit of this invention, Reference is theretore to be had to the claims hereto appended for a denition of the limits'of the invention. p p What is claimed is; e 1. The method oftesting a thin strip of material by subjecting the same to repeated and reversed bending stresses which includes alternately bending said strip progressively upon opposedcurved surfaces while exerting a tensile stress lengthwise of said strip, and automatically varyng the magnitude of said tensile Stress during the progression of said bending. a

2. The method of determining the endurance limit of thin e material under simple bending stresses which i includes subjecting i eachof a pluralityj of thinstrips of the mai terial to repeated and reversed bending stresses until ruptured upon a pair of curved surfaces, the respective strips being subjected to surfaces of diffrent radii of curvature. 3. The method of determinng the endurance limit of thin material .under simple bending stresses which includes subjecting each of 'a plurality of thin strips of the material'to repeated and reversed bending stresses until ruptured by progressively bending each strip to predetermined curvature, the respective strips being curvature. A

4. The method of determining the endurance limit of thin material under simple' bending stresses which includes subjecting each of a plurality of thin strips to repeated and reversed bending stresses by subjecting each strip to the action of a pair of opposed oscil- Iating curved surfaces until ruptured, said surfaces *having different radii of curvature and reversed bending tests, a pair of members having opposed surved surfaces of the same curvature, means for attaching a test piece at'ts opposite ends to the respective members, and means for continuously oscillating said members alternately in opposite directions to alternately bend the test piece oppositely to equal extents upon the respective surfaces. e

7. In a machine for testing thin strips of material by subjecting the same to repeated i and reversed bending tests, a pair of members having opposed circularly curved adjaent surfaces, means for attaching the test piece atits opposite ends to-the respective members to hold said test piece in an ogee '40 curve, and means for oscillating said members to bend the test piece alternately and equally along its length upon the respective surfaces.

8. In a machine for testing thin strips of material by subjecting the same to repeated and reversed bending tests, a pair of members having curved adjacent surfaces, means for mounting said members osc llatably With 4. i said curved surfaces in oppos tion, and means for continuously oscillating said members simultaneously. f

9. In a machine for testing thin s trips of material by subjecting the same to repeated and reversed bending tests, means for supporting pairs of members having opposed curved surfaces, means for attaching a 'test piece to said members at its opposite ends, andmeans for'continuously oscillating said members to bend the test piece alternately upon said opposed surfaces, said last-named means -cooperating Withsaid members to pro duce equal rates 'of movement thereof.

10. In a machine for subjecting thin strips of material` to repeated and reversed bending tests, means for supporting pairs of members bent to different radii of having opposed curved surfaces, means for' attaching a test piece to said'members at its opposite ends, means for oscillating said members to bend the testpiece alternately upon said opposed surfaces, and means for adjusting'said supporting means to accommodate pairs of members having surfaces of different radii of curvature.

ll. In a machine for subjecting thin strips of material to repeated and reversed bending tests, means for supporting pairs of members having opposed curved surfaces, means for attaching a test piece to said members at its opposite ends, means for oscillating said members to bend the test piece alternately upon said opposed surfaces, and means for adjusting said supporting means to render the rate of oscillation of said members unequal.

' 12. In a machine for subjecting thin strips of material to repeated and reversed bending tests', a pair of support-s adapted to carry members having opposed curved surfaces,

means for adjusting said supports toward andfrom each other, means 'for attaching a test piece at its opposite ends to said members, and means for oscillating said members to alternately bend the test piece upon said opposed curved surfaces.

13. In a machine for sub-jecting thin strips of material to 'repeated and reversed bending tests, a pair of supports adapted to carry members having opposed curved surfaces, neans for adjustng said supports' toward and from each other, means for adjusting both of said supports in the same' direction, means for attaching a testpiece at its opposite ends to said members, and means for osc'illating said 'members to 'alternately bend the test piece uponsaid opposed curved surfaces.

14. In a machine' for testing thin strips of material by subjecting the same to repeated and reversed bending tests, a pair 'of supports for mounting 'pairs of members having opposed closely adjacent curved surfaces, and means for oscillating said members in opposite? directions and at equal rates of movement. y

15. In a machine for subjecting thin strips of material to repeated 'and reversed bend ing tests, a' pair of supports for mounting pairs of members having opposed curved surfaces, means for oscillating said members, and means for adjusting said supports to 'accommodate different pairs of members having curved surfaces of different radii of curvature.

16. In a machine for subjecting thin strips of material to repeated and reversed bending tests, a pair of supports for mounting pairs of members having opposed curved surfaces, means for oscillating said members, and means for adjusting said supports With respect to said oscillating means-in order to means for counting the number esasoa rendor the rate' o'f os'cillation of said members unequal. a e

17. In a machine for subj eeting thin strps of material to repeated and reversed bendf ing tests, a pair of supports for mountmg pairs of members having opposed curved surfaces, means for oscillating said members, means for adjusting said supports to accommodate pairs ofmembers having; curved I surfaces of different radii of curvature, and

means for adjusting said supports to `enable said oscillating means to efiect' difierent rates of oscillation' of said members.

18. In a machine for subjecting thinstrips of material to r epeated and reversed bending tests, a pair of members having opposed curved surfaces, means' for attaching a test piece at its opposite ends to said members,"`

` curved surfaces, means for attaching a test piece at its opposite ends to said opposed surfaces, means for oscillatmg said members, means for counting the number of oscillations ofsaid members, and means actuated b 'the breaka 'e of the test ecewhere-` by the ?number of oscillations required to break the same may be noted;

20. In a machine for testingthin strips of material by subjecting the same to repeated and reversed bending test-s, a pair of supports adapted to pivotally support pairs of members having opposed curved surfaces, a rectilinearly movable member, *and means connecting said rectilinearly movable member With said pivotally mounted members at opposite sides of their respective pivotal anes Whereby reciprocation of said rectilinearly movable member is accompanied by simultaneous oscillatory movement ofsaid members around their aXes in oppo'site directions.

21. In a machine for subjecting thin strips of materia-l to repeated and reversed bending said supports to accommodate oscil atory members of different sizes, V

22. In a machine forsubjecting 'thin strips of material to repeated and reversed bending tests, a pair of supports adapted to piv- ,otally support pars of members having opposed curved 'surfaces, a 'rectilinearlvmovable member, means;connectingoosaid rectilinearly movable member ith saidpivotally mounted members at opposite sides-of their` respective pivotal axes, anduneans'for adjusting said supports simultaneously and:

equally to maintain the same angular relation of said connecting meansto the line of reciprocaton of said' rectilinearly movable member.

23; In a-machine for subjecting thin strips i of material to repeated and reversed bending tests, apair of supports adapted to pivotally support pairs of members having opposed` curved surfaces, a rectilinearly movable member, means connecting said rectilinearly movable member With said pivotally mounted members at opposite sides of their respective pivot-al axes, and means to adjust said supports to vary the relative angularity of said connectng means to the line OI" rec1procation of said rectilinearly movable member.

24. Ina machine for subjecting thin strips of material to repeated and reversed bending tests, a pair of supports adapted to pivotally support pairs of members having opposed ber, means connecting said rectilinearly movable member with said opivotally mounted members at opposite sides of their respective pivotal aXes, and meansto adjust said resti linearly movable member to maintain a pre: determined relationship between the oscillatory members as oscillatory members of different sizes are mounted on said supports.

25. In a machine for subjecting thin strips curved surfaces, a rectilinearly movable memi of material to repeated and reversed bending tests, a pair of supports for mounting pairs of oscillatory members With opposed curved surfaces, means for oscillating said, members, means including a crank mechanism for driving saidoscillating means, and means for adjustingsaid crank mechanism.

26. In a machine for subjecting thin strips of naterial to repeated and reversed bending tests, a pair of supports for mounting pairs of oscillatory members With opposed curved surfaces, meansfor oscillating said nembers including a crosshead and links con necting said crosshead to said oscillatory members, and means for adjusting said' crosshead relatively to said supports of said osci'l-o latory members. I

27. In a machine for subjecting thin strips of material to repeated and reversed bending tests, a pair of supports for mounting pairs of oscillatory members With opposed curved surfaces, means 'for oscillatng said members,

and equally pitched right and left hand multaneously adjusting said supportstoward and from each other, and adjustable bearings for said rod for simultaneously adjusting said supports and said rod in the same direction. 29. in a machine forsub ectmg thin strips of material to repeated and reversed bending` test-s, means for supporting pairs of members having opposed curved surfaces, means for for oscillating said members, and means for attaching a test piece to said members at its opposite ends, said attaching means including a device for imposing a tensile stress on said test 'piece as it lS alternately bent upon said respective curved surfaces.

` 31. In a machine for subj ectng thin stripsof material to repeated and reversed bending tests, means for supporting pairs of memt bers having opposed curved surfaces, means for oscillatin said members, means for attaching a test piece to said members at ts opposite ends, said means including an arm pivoted to oneoi' said oscillatory members and clamping means carried by said arm, and means reacting between said arm and its oscillatory member for exerting a pull on a test piece clamped to said arm. r

32. In a machine for subjecting thin strips of material to repeated and reversed bending tests, means for supporting pairs of members having opposed curved surfaces, means or oscillating said members, means for attaching a test piece to said members at its opposite ends, said means including aclampmg arm pivoted to one of said oscillatory 1nembersand clamping means -carried by said arm, a spring reacting between said arm and its oscillatory member, and means for adjust ing said spring. i i

33. In a' machine for subjecting thin strips of material'to repeated and reversed bending tests, means for supporting pairs o' members having opposed curved surfaces, means for oscillating said members, means for attaching a test piece to said members at its opposite ends, and means for exerting a variable tension on a test pece clamped to said oscillatory members as the test piece is alter nately bent upon the respective curved sur faces. v v.

34. The method of testing a thin strip of sheet material which includes subjecting the strip to repeated and reversed bending stresses by oscillating a pair of opposed members having surfaces of equal radius of curvature which is large as Compared with the length of the actively tested portion of said strip and alternately bending said strip upon the respective curved surfaces to stress,

said strip oppositely by equal amounts. v

A 35. The method of testing a thin strip of sheet material which includes subjecting the strip to repeated and reversed bending stresses by oscillating a pair of opposed curved segmental members and alternately bending said strip .upon said curved members while exerting a tensile stress lengthwise of said strip.

36. The method of testing a thin strip of sheet material which includes subjecting` the strip to repeated and reversed bending stresses by bending said strip first upon one and then upon the other of a pair of curved segmental members while exerting a constant tensile stress lengthwise of said strip.

37. A method of testing sheet material by causing a simple reversed bend to periodically traverse the material, while subjecting the same to synchronously varied tension.

38. Themethod of testing a thin strip of metal which includes subjecting the Same to repeated and reversed bending stresses by alternately bending the strip in opposite directions into arcs of substantial radius of curvature but which arcs do not e ceed semi-circles. 39. The method of testing a thin strip' of sheet material which includes subjecting the strip to repeated and reversed bending stresses by alternately bending the strip upon opposed oscillating curved members to defiect said strip through arcs of substantial radii of curvature and not exceeding 180.

410. The method of testing a thin strip of sheet material which includes subjecting the strip to repeated and reversed bending stresses by'oscillating a pair 'of opposed curved members and alternately bending said strip into segmental arcs whose combined lengths approXimate that of the portion of the'strip being actively tested upon the respec'tive curved surfaces to stress said strip in opposi'te directions. i

il. The method of testing a thin'strip of sheet' material 'which includes subjecting the strip to i repeated and reversed bending stresses by progressively bending the strip from end to end of the stressed portion and alternately 'in opposite directions into arcs whose combined lengths approximate that of the portion of the strip being actively tested. p

42. The method of testing a thin strip of sheet material which includes subjecting the .strip to repeated and reversed bending stresses by alternately bending the strip in' opposite directions into segmental' arcs upon curved members whose radii of curvature are large as Compared with the length of the actively tested portion of the strip while exerting a tensile stress lengthwise of said strip. 43. The method of testing a thin strip of material which includes subjecting the same to repeated and reversed bending stresses by alternately bending the strip in opposite directions to less-than-circular arcs of fixed and predetermined curvatures the radi of which' are large as Compared withthe length of the strip being actively tested.

44:. The method of testing a thin strip of sheet material which includes subjecting the strip to repeated and reversed bending stresses by alternately bending the strip on a pair of opposed oscillating'curved members into arcs of substantial radii of curvature and less-than-circular eXtent. I

45. A method of testing sheet material by causing a simple reversed'bend to periodically traverse the material from end to end of the actively tested portion to form arcs whose combined lengths approximate that of the actively tested portion of the strip.

46. A method of testing sheet material by causing a simple reversed bend to periodically traverse the material to form arcs whose combined lengths approximate that of the actively tested portion of the strip While subjecting the same tovtension.

47. A method of testing sheet material by causing the material to reciprocate in a fixed path providing reversed directions of curvature in arcs whose len th approxmates that of the length of the actively tested portion of the strip. r

48. The method of testing a thin strip of material which includes subjecting the same to repeated and reversed bending stresses by alternately and oppositely bending the strip in the direction of its thickness into segmental arcs of fixed curvature and whose combined lengths approximate the length oi the actively tested portion of the strip.

49. The method of testing a thin stripof sheet material which includes subjecting the strip to repeated and reversed bending= stresses by alternately bending the strip in,

opposite directions into segmental arcs upon opposed oscillating curved members whose length approxmates that of the actively tested portion of the strip.

50. The method of testing a thin stripof e sheet material which includes subjecting the strip to repeated and reversed bending stresses by progressively and alternately bending the strip from end to end of the stressed portion into opposite arcs whose combined lengths approximate the length, of

the actively tested portion of the strip while exerting a tensile stress lengthwise of said strip.

In testimony whereof I have signed this specification.

" JEAN V. GIESLER. 

